Belgium Pat. No. 899,399 describes certain 7-piperazine-1-cyclopropyl-6,8-difluoro-1,4-dihydro-4-oxo-3-quinolinecarbo xylic acids. German Offenlegungschrift 3318145 describes various 7-amino-1-cyclopropyl-6,8-difluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acids. European Pat. Publication No. 106489 describes 7-cyclic amino-1-cyclopropyl-6,8-difluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acids.
All of the above compounds are useful as antibacterial agents and have been described as being prepared by displacement of a 7-fluoro atom from a compound of the formula ##STR1## wherein X is hydrogen or fluorine; R.sub.1 is hydrogen or lower alkyl, and R.sub.2 is alkyl of one to three carbon atoms or cycloalkyl of three to six carbon atoms, with the appropriate amine.
The object of the present invention is an improved process for preparing the compounds described above using a 1-alkyl or cycloalkyl-6,7,8-trifluoro-1,4-dihydro-4-oxo-quinoline-3-carbonitrile for the displacement reaction with the appropriate amine and then hydrolysis of the nitrile group and any protecting group present to give the final product.
The present method provides better quality material with fewer purification procedures, step-saving by being able to carry out the reaction in fewer "pots," and high overall yields from tetrafluorobenzoyl chloride.